The present invention relates to an apparatus and a method to treat a disease process in a luminal structure. Such a structure includes, but is not limited to, veins, arteries, bypass graft prostheses, the gastrointestinal (GI) tract, the biliary tract, the genitourinary (GU) tract, and the respiratory tract (e.g. the tracheobronchial tree).
Within this application several publications are referenced by Arabic numerals within parentheses. Full citations for these and other publications may be found at the end of the specification immediately preceding the claims. The disclosures of all of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
Percutaneous transluminal coronary angioplasty ("PCTA") is commonly used in the treatment of coronary artery obstruction, with over 400,000 procedures performed annually. The process involves the insertion of balloon catheters through the femoral artery to the targeted coronary artery. Injection of radio-opaque contrast into the proximal coronary artery allows fluoroscopic localization of stenosed coronary segments. Balloon catheters are advanced to the site of stenosis over extremely thin guide wires to position the catheter at the point of occlusion. The distal end of the catheter contains a balloon which is inflated for 2-4 minutes to the full diameter of the occluded artery, decreasing the blockage and improving blood flow.
Approximately 40% of patients undergoing this procedure have angiographic evidence of restenosis by 12 months. The biological processes responsible for restenosis are not fully understood, but appear to result from abnormal proliferation of the "insulted" smooth muscle cells and neointima formation in the segment of treated artery (6). Although coronary artery blockage is a non-malignant disease, it has been suggested that treatment of the internal vessel walls with ionizing radiation could inhibit cell growth, and delay or even prevent restenosis (4, 7, 10-13).
Several groups have presented data demonstrating that 10-20 Gray of acute radiation delivered locally, via the temporary insertion of high activity gamma emitters at the time of angioplasty can inhibit restenosis in animal models (12,13). It has also been demonstrated that permanent radioactive coronary stents may be effective (10). Highly localized external beam therapy has been suggested as well (7,11). Most data to date have been obtained using animal models, but anecdotal reports suggest that radioactive treatment of human femoral arteries produces similar results (2). Preliminary human trials are being planned at several centers in the U.S. and Europe.
Preliminary studies have made use of currently available radioactive sources as none have been specifically designed for intracoronary treatments. Several manufacturers are considering modified High Dose Rate (HDR) afterloaders for this purpose.
As stated above, restenosis after arterial intervention in general, PTCA in particular, seem to be primarily due to medial smooth muscle cell proliferation. Conventional PTCA is performed using a balloon catheter such an over-the-wire type catheter manufactured, for example, by Scimed Life Systems, Inc, of Maple Grove, Minn. or a mono-rail type catheter manufactured, for example, by Advanced Cardiovascular Systems, Inc, of Temecula, Calif. FIG. 1 depicts such a conventional over-the-wire balloon catheter 1. The conventional balloon catheter 1 is utilized in an angioplasty procedure as follows. A conventional guidewire 2 is inserted into the patient's artery until the distal end of the guidewire 2 is past a target area (not shown) of the artery (not shown) where there is a buildup of material. The conventional balloon catheter 1 has a lumen 3 running therethrough. The guidewire 2 is inserted into the distal end of the balloon catheter 1 and the balloon catheter 1 is advanced over the guidewire until the balloon section 1a of the balloon catheter 1 is adjacent the buildup of material. The balloon section 1a is then inflated by an inflation means (not show) connected to an inflation port 1b to clear the artery. Finally, the balloon section 1a is deflated, the balloon catheter 1 is pulled back up the guidewire and removed and the guidewire is likewise removed from the patient's artery.
Current technology contemplates different types of devices for the prevention of restenosis after arterial interventions. In one type, an arterial stent type is designed for long term deployment within the artery. Such a stent, if designed to emit radiation, would be in place long after the time necessary for the prevention of smooth muscle cell proliferation at the arterial site. U.S. Pat. No. 5,059,166 to Fischell describes such a long term stent.
Another type of device for preventing restenosis contemplates the delivery of unspecified doses of radiation via radioactive catheters and guidewires. These devices utilize a movable, flexible radiation shield. However, it is questionable whether such a radiation shield could be constructed given the thickness of material required to shield the radiation source and the flexibility required to allow delivery of the radiation source and shield to the coronary site. U.S. Pat. No. 5,213,561 to Weinstein relates to a device of this type.
Another type of device uses radioactive balloons which are typically inserted into a luminal structure in a deflated condition, and inflated with radioactive fluid after insertion. After a treatment period, the fluid is evacuated from the balloon and the device is removed. With such a system, there is always the risk that the balloon could rupture or leak resulting in radioactive fluid passing into the luminal structure.